We propose to continue our current project on the physiology of the hypothalamic neurohormones which regulate secretion of pituitary hormones. Emphasis will be placed on delineating the release of growth hormone releasing hormone (GHRH), prolactin releasing hormone (PRH), and corticotronin releasing hormone (CRH) into the rat hypohyseal portal blood and determining characteristics of these hypothalamic hormones. Pituitary hormone releasing activity will be measured using a multichannel perifusion system followed by measurement of the pituitary hormones in the perifusion output by the appropriate RIA. If such activities are present in the rat hypophyseal portal blood, we will assess the hormone releasing activity of portal blood following electrical stimulation of various regions of the brain known to stimulate the release of the respective pituitary hormone and intraventricular injection of various neurotransmitters. This will serve as a preliminary assessment of the physiological importance of the observed hormone releasing activity and will provide releasing hormone-enriched portal blood. The enriched portal blood will then be pooled, extracted and the physicochemical characteristics of the active substances examined. In parallel studies, the physico-chemical properties of active substances obtained from hypothalamic extracts of rats and domestic animals and from rat hypophyseal portal blood will be compared. If any fraction is found to contain significant GHRH, PRH, or CRH activity, an effort will be made to isolate these hormones. Extracts of pancreatic and gut tissue from rats and domestic animals will also be examined for these releasing activities. If any extrahypothalamic fraction is found to possess these activities an effort will be made to isolate these substances, and their physico-chemical properties compared to those of active substances found in rat hypophyseal portal blood and hypothalamic extracts.